In recent years bi-directional overrunning clutches have been incorporated into various drive systems to replace conventional differentials. Conventional differentials include: open, limited slip, locking and center differentials. U.S. Pat. No. RE38,012, commonly owned by the assignee of the present invention, describes a bi-directional overrunning clutch for controlling torque transmission between a secondary drive shaft and secondary driven shafts. This transmission system is beneficial in four wheel drive vehicles where it is desirable to be able to engage and disengage the secondary driven shafts in different driving environments. The system described in U.S. Pat. No. RE38,012 includes an innovative system to advance and/or retard a roll cage, thereby controlling the ability of the differential to engage and disengage depending on the operational state of the primary and secondary wheels. The system includes an electro-mechanical device, which in one embodiment is an electrically controlled coil adjacent to an armature plate that is engaged with the roll cage and rotates in conjunction with the roll cage. When the coil is energized, an electromagnetic field is produced which hinders the rotation of the armature plate, thus causing the roll cage to drag or advance into an appropriate position relative a clutch housing.
The differential in U.S. Pat. No. RE38,012 also includes a unique backdrive system. The backdrive system actively engages the secondary shafts in certain situations where extra traction is needed. For example, when the vehicle is driving down a slope the system engages the front wheels, which are the wheels with the better traction.
U.S. Pat. No. 6,622,837, commonly assigned to the assignee of the present invention, describes a differential system that includes a bi-directional overrunning clutch with automatic backdrive capability. In this system, an electromagnetic device is used to engage an armature plate that is keyed into the roll cage through tangs. Energizing of the electromagnetic device attracts the armature plate causing it to drag the roll cage, thereby placing the clutch in the activated position for four wheel drive. In another embodiment, a hydraulic piston engages the roll cage causing it to drag.
U.S. Pat. No. 6,629,590, commonly assigned to the assignee of the present invention, describes a spring assembly for a roll cage in a bidirectional overrunning clutch. The spring assembly includes multiple H-clip springs mounted to the roll cage with each H-Clip spring comprising a bridge with spring arms mounted in each end of the bridge and positioned in a slot of the roll cage. The spring arms function to bias the rolls into the center of the slot, the result is the H-clip springs provide a spring force to bias the roll cage into its neutral position. The configuration of the springs also are designed to overcome manufacturing tolerances so as to result in all the rolls engaging at the same time.
An alternate roll cage spring adjustment assembly has been developed by the assignee of the present invention and on the market for a few years. The roll cage and spring adjustment assembly is illustrated in FIG. 1 and includes a roll cage assembly with a plurality of rolls 2 mounted within slots in a roll cage 1. The roll cage assembly is mounted within a clutch housing 3 as described in U.S. Pat. No. 6,629,590. An actuation system with a coil (not shown) and armature plate 4 was mounted to the clutch housing 3 for controlling rotation of the roll cage into its four wheel drive operating mode. The operation of the coil and armature plate was similar to the system described in U.S. Pat. Nos. RE38,012 and 6,629,590. In order to bias the roll cage into its neutral position, the system included a torsion spring 5 that was mounted to an end of the roll cage 1. The spring includes two radially extending arms 6 that projected past the outer circumference of the roll cage 1. When the roll cage was mounted within the clutch housing 3, the arms 6 projected outward and through a slot 7 cut into the clutch housing 3. The arms seated against the radial faces 8 on the circumferential ends of the slot 7. As such, any rotation of the roll cage relative to the clutch housing would cause the arms 6 to bear into the faces 8, thus deforming the torsion spring. This resulted in the torsion spring to bias the roll cage back to its neutral position.
A need still exists for an improved engagement system that provides consistent activation of the clutch while preventing inadvertent engagement and undesirable wedging.